1. Field of the Invention
This invention generally relates to apparatus that can be used to humidify air and more specifically to apparatus that uses an immersion heater for converting liquids into gas as, for example, by generating steam for use in humidifiers.
2. Description of Related Art
Humidifiers, distilling apparatus and like apparatus use immersion heaters to convert a liquid, such as water, into vapor or steam by boiling water. In humidifiers the steam mixes with air and disperses throughout a room to increase relative humidity. In a distilling apparatus a condenser receives the steam to produce distilled water.
There are many embodiments of such apparatus. Generally, however, warm mist humidifiers and distilling apparatus include some type of immersion heater. Characteristically over time deposits or residues from the water adhere to the surface of such immersion heaters. More specifically, water available through various municipal and other supplies contains minerals that do not evaporate along with the water. Certain of these minerals, especially lime, adhere to the heat transfer area, namely to the outer surface of the immersion heater. As the residue accumulates, the heat transfer rate to the water decreases with two adverse effects. First, the process by which the boiling occurs becomes less efficient. Secondly, the heating coils operate at a higher temperature. Moreover, as also known, the residue becomes more difficult to remove after it accumulates over time.
U.S. Pat. No. 5,343,551 (1994) to Glucksman discloses one embodiment of an immersion heater used with a portable air humidifier. A housing contains an evaporation chamber in the shape of an inverted cup. The chamber has a steam outlet in its top and an electric heating element positioned a short distance above an open bottom. In this particular humidifier a blower delivers cool air through a duct to communicate with the evaporation chamber through its steam outlet to blow humidified air back into the room. Water from a main compartment or tank transfers to a compartment in a removable tray that allows ready access to the compartments for cleaning.
U.S. Pat. No. 4,818,344 (1989) to Glucksman discloses a water distilling apparatus with a vaporization chamber containing an electric coil heating element, a fin tube condenser coil and an electric fan for cooling the surfaces of the condenser coils. An electric coil heating element vaporizes water and the resulting steam travels through the condenser tubing where it is reconverted to pure water and delivered to a beaker through a water outlet. Various portions of this device can be removed for cleaning sediments and residues.
U.S. Pat. No. 5,835,680 (1998) to Glucksman et al. discloses an immersible heater with an annular collar that spaces a heating element above a bottom wall of the structure. The collar acts as an insulator thereby to limit the heat transferred to the bottom wall that is typically formed of a plastic material. In addition, a thermostat monitors the temperature of the heater. When the water is nearly evaporated, the thermostat or a backup thermofuse turns off the heater. This occurs while water still surrounds at least the collar and therefore further prevents damage from overheating.
In another humidifier sold by Slant Fin a stainless steel cup holds water to be boiled. A heating coil attaches to the exterior of the cup and heats the water in the cup to the boiling point. The interior of the cup is more readily cleaned than prior cups. However, like the other devices described above, it is necessary to handle an entire base unit. However, such base units generally contain electrical components. It is generally recommended that they not be immersed in water or cleaned in a dishwasher.
Each of the foregoing patents discloses a humidifier or water distilling apparatus on which it is difficult to remove and clean residue that adheres to the heating element. The use of stainless steel cups reduces the effort required to clean a heating element. However, such heating elements are usually integral with a base unit and hard to reach. In others the heater is made more accessible. However an entire base unit must be moved to a sink or other cleaning area. The base unit generally includes electrical components so it can not be immersed in water. Consequently, individuals do not clean such devices on a regular basis even though this means that the operating efficiency for the apparatus is degraded.
Prior apparatus, particularly prior humidifiers, have other operating deficiencies. For example, a requirement to heat large volumes of water increases the time that lapses between the application of power to and the generation of steam by the humidifier. Large volumes of water also can pose a risk if the humidifier tips and discharges hot water as all the water is heated and potentially injurious. In others, the boiling process can cause spurts of hot water to eject from the humidifier causing proximate furniture or carpets to become soiled.